Gtk.Image set_pixel_size stopped scaling image in GTK 4.19.2

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Hi all,

I’m developing a GTK app, built as a Flatpak using GNOME Nightly.

In my UI, I use a custom button-like widget that contains a child Gtk.Image. As the window is resized, the widget and the image should scale dynamically. To handle this, I’ve overridden the size_allocate function to:

  • Calculate the new size for the image
  • Call size_allocate() on the image to resize it
  • Call set_pixel_size() on the image to scale it

This setup had been working fine. However, starting today, I noticed that the image now appears very blurry. I suspect this change is due to a recent update in GTK brought in through GNOME Nightly.

I could not pinpoint the exact commit but I found this GTK 4.19.2 NEWS update which seems related to the behavior I’m seeing:

* GtkImage:
 - Change the sizing behavior for paintables. Stop scaling them up

So my questions are:

  • What’s the correct approach now for dynamically scaling images with Gtk.Image?
  • Can I still achieve this effect using Gtk.Image, or do I have to resort to a lower-level API like Gdk.Texture or Gdk.Paintable directly?
1 Like
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Did you try using gtkpicture instead? But I tried gtkimage a bit now too and there seems to be something weird going on as it scales in height. It’s this mr: iconhelper: Stop scaling up paintables (!8627) · Merge requests · GNOME / gtk · GitLab

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I’ve currently pinned my flatpak manifest to GNOME 48 until I have more time to properly address this. The MR does indeed suggest using Gtk.Picture for scalable icons, so I’ll move towards that direction I guess.

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There may be a typo on this line, width should probably be w: gtk/gtkiconhelper.c · main · GNOME / gtk · GitLab

This does not help with this topic though, gtkpicture should be used for scaling images.

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